1. Field of the Invention
The present invention relates in general to friction type clutches or brakes including electromagnetically operated disengaging means wherein an armature with a driving friction ring is moved into and out of engagement with the friction elements associated with the output means and specifically to adjusting the air gap between the armature and the magnetic pole faces.
2. Description of the Prior Art
In prior art clutches or brakes of this type, the disengagement of the clutching members is affected by a solenoid disposed in an axially stationary component (magnetic core) of the clutch or the brake. The magnetic field generated by the solenoid, overcoming the force of the clutch or the brake springs, attracts the axially displaceable armature across an air gap and this removes the pressure exerted by the springs on the friction elements.
Several prior art devices are directed toward the problem of automatically adjusting the air gap to compensate for wear of flat friction elements (U.S. Pat. Nos. 3,458,022; 3,485,330; 3,613,849; and 3,857,468). In U.S. Pat. No. 4,030,583 to Miller, owned by the assignee of the present invention, an electric cone clutch is disclosed wherein the air gap is maintained in a fixed position and the relative position between the armature and the friction ring is maintained by a retarder disposed coaxially with the armature. None of the above prior art designs provides for an easy adjustment of the initial air gap so that it is responsive to a fixed level of electromagnetic flux generated in the magnetic coil. Furthermore, it is a disadvantage of the aforementioned prior art structures that production tolerances must be closely maintained to obtain the initial air gap setting within specific limits. It is a further disadvantage of the prior art clutches that when the voltage required to disengage the clutch exceeds enginerring specifications, the clutch must be disassembled and shims installed therein to reduce the air gap in order to permit the clutch to disengage within the specified voltage limitation.